A problem which has long existed in the paper industry is that titanium dioxide used to enhance whiteness and opacity in paper is not readily retained by the cellulosic fibers of the paper. One solution to this problem is set forth in U.S. Pat. No. 2,992,964 which discloses coating alkyl ketene dimers on titanium dioxide. Such patent states that the coated titanium dioxide exhibits improved retention on the cellulosic fibers of the paper.
While this patent discloses an advance in the art, it would be desirable to have a process which would enhance sizing of the paper and increase the rate of size development. As used herein, "size" refers to the ability of a paper to resist adsorption of aqueous ink. A paper with good sizing will require a longer time for the ink to be adsorbed than a paper with poor sizing. Improved rate of size development (i.e., the final size developed by the paper) is also important because if the rate of size development is slow, this makes it difficult to adjust promptly the paper making conditions to optimize the desired amount of sizing.
It would also be desirable if the coated titanium dioxide would exhibit improved retention on the cellulosic fibers of the paper.
Moreover, it would be desirable if the coating of the titanium dioxide could take place during the formation of an aqueous dispersion of the titanium dioxide.
Reference is also made to the following patents which may be of interest to this invention:
U.S. Pat. No. 4,522,686 discloses aqueous dispersions of hydrophobic cellulose reactive sizing agents, such as ketene dimer, fortified with resin and a water-soluble, nitrogen-containing cationic dispersing agent.
U.S. Pat. No. 3,702,733 discloses preparing aqueous slurries of TiO.sub.2. A portion of the TiO.sub.2 is steam micronized in the presence of an alkanol amine.